Solar Reflectance
Solar Reflectance is the fraction of the incident solar energy which is reflected by the surface in question. The best standard technique for its determination uses spectrophotometric measurements, with an integrating sphere to determine the reflectance at each different wavelength. The average reflectance is then determined by an averaging process, using a standard solar spectrum. This method is documented by ASTM (American Society for Testing and Materials) as Standards E903 and E892. When this data is not available, other, less detailed measurements are utilized. The visible reflectance is sometimes measured by manufacturers. This is the reflectance in the visual part of the solar spectrum, wavelengths of 400 to 700 nanometers. Usually the visible reflectance is correlated with the solar reflectance, but the two quantities are not equal. For example, a good white coating with a solar reflectance of 0.8 typically has a visible reflectance of about 0.9.1
Infrared Emittance
Infrared Emittance is a parameter between 0 and 1 which measures the ability of a warm or hot material to shed some of its heat in the form of infrared radiation. The wavelength range for this radiant energy is roughly 5 to 40 micrometers. Most building materials (including glass!) are opaque in this part of the spectrum, and have an emittance of roughly 0.9. Materials such as clean, bare metals are the most important exceptions to the 0.9 rule. Thus clean, untarnished galvanized steel has a very low emittance, and aluminum roof coatings have intermediate levels of emittance. A material with an emittance of unity ("black body"), emits about 6.1 watts per square meter, for each degree C above ambient temperature.1